The construction of mechanism maps for hot-isostatic pressing is described. Maps are constructed for a number of materials of commercial and scientific interest: a tool steel, a superalloy, Al2O3, and ice. They allow the processes involved in hot-isostatic pressing to be examined, and suggest ways of picking optimum combinations of pressure, temperature, and time to give maximum density.

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Practical applications of hotisostatic Pressing diagrams: Four case studies

The status of rapid solidification is discussed in terms of recent progress in modelling methods of achieving solidification at high cooling rates and its effects on alloy constitution and microstructure. Applications currently in view are reviewed under the following headings: high-strength structural materials; tool and bearing materials; high-temperature materials, corrosion-resistant, catalytic and storage materials; and electrical and magnetic materials. It is concluded that the future of rapid solidification is not identifiable with any one process, activity or application and that many unresolved questions remain to challenge both the scientific and business communities.

The status of rapid solidification of alloys in research and application

The potential of spray forming (SF) for microstructural refining can be attractive to the production of high speed steels. The refined as-cast structure may lead to important improvements of material properties, compared to conventionally cast materials. The present work aimed to compare the properties of AISI M3:2 high speed steel produced through spray forming and conventional casting. Also, the processing of SF billet is considered, specifically the hot working conditions and its relation to carbide size. A round 400 mm diameter SF billet was produced using a twin atomiser. Characterisation was performed in the as-cast structure and after hot working to 116 mm squared bars and 11 mm diameter round bars. The results show that, compared to conventionally cast high speed steel, the SF material has higher isotropy in toughness due to its less oriented carbide distribution. Regarding processing procedures, time and temperature employed in heating before hot working also affect the microstructure of SF material.

Spray forming high speed steel—properties and processing

Overview of Rapid Solidification Technology

The work is aimed at describing the influence of thermal treatment on the properties of a tool steel containing (in wt.%) 2.5% C, 3.3% Si, 6.2% Cr, 2.2% Mo, 2.6% V, 2.6% Nb, 1.0% W prepared by the powder metallurgy process. Alloying with niobium positively affects the microstructure, the mechanical properties and the performance of the steel. The microstructure of the hardened steel is composed of a martensitic matrix, retained austenite and various types of carbide. During tempering of the hardened steel at the temperatures above 480 °C precipitation of very fine carbides occurs, which results in secondary hardening. The optimum thermal treatment of the steel is austenitisation at 1050–1100 °C, nitrogen cooling and tempering at 540 °C (3×1 h).

Thermal treatment of PM-tool steel alloyed with niobium

The ‘KHA process’ for producing PM high-speed steels using gas-atomizing equipment and the hot isostatic press has been developed by Kobe Steel Ltd. Measurement of the secondary dendrite arm spacing of gas-atomized powders indicated that the relation between the dendrite arm spacing S II (μm) and the powder particle diameter d (m) was described by S II= K□d where K is a constant. To establish suitable hot isostatic pressing (HIP) conditions with high productivity, density and bending strength were studied in relation to various HIP conditions. It was found that, for example, the combination of 1373K, 40MPa, 30 min was sufficient to obtain full density, but that 1473K, 40MPa, 30min was required to obtain the maximum bending strength. By studying various properties of KHA high-speed steels, it was found that they were superior to the conventional steels for toughness, grindability, and hot workability. Tools such as drills, end mills, hobs, etc. produced from KHA materials exhibited better cutting p...

N. Kawai

Papers

Properties of High-Speed Steels Produced by Powder Metallurgy